Ice Zones: Where We Look for Ice

Overview

In this 30 minute activity, children, ages 8 to 13, draw conclusions about where on a planetary body scientists might look for ice — and why. They use a clay ball, ice cubes, and a heat lamp to model the permanently-shadowed polar regions of planets and moons that may harbor ice. They learn that our Moon and even Mercury may have areas with ice!

What's the Point?

Polar regions of most planets and moons receive less intensive solar radiation primarily because the Sun's radiation strikes the surface at an oblique angle and spreads over a larger area.

Equatorial regions of most planets and moons receive more intensive solar radiation primarily because the Sun's incoming energy strikes the surface at a perpendicular angle; the sunlight is more direct.

Planets and moons that lack a moderating atmosphere have temperatures below freezing point of water on surfaces facing away from the Sun. These same surfaces may be heated to well above the boiling point of water when they rotate into sunlight.

Areas on a planet or moon that are in permanent shadow can maintain very cold temperatures, even on planets that are close to the Sun.

Permanently shadowed regions can occur in craters near the poles of planets and moons that have very small tilt of their axes, such as the Moon and Mercury.

Ice may exist in these permanently shadowed regions.

Materials

For each group of three to four children:

1 heat lamp or work lamp with a 100 watt or greater light bulb

1 (6" or larger) clay ball (or Styrofoam ball covered with clay)

1 paper plate

16 toothpicks

2 ice cubes of similar size

Small Styrofoam or insulated cup or container to keep the ice cubes frozen (optional)

Preparation

The activity, as presented, focuses on why some moons and planets may have permanently shadowed regions at their poles, and explores that these regions offer conditions in which ice can exist. The activity also offers many opportunities to explore day and night and seasonal cycles on Earth and other planets.

The activity can be done as a demonstration.

Activity

1. Invite the children to share their ideas about ice.

What conditions does ice need to exist? Temperatures need to be cold.

Where in our solar system are the temperatures cold? Far from the Sun.

Earth's average temperature is above freezing according to the image. How can it have ice? The image shows average temperatures, so some temperatures can be warmer and some can be colder.

Earth is pretty close to the Sun, how can we have cold areas with ice and snow? Some children may share that the polar regions get less sunlight; this will be explored in the activity. Others may say that we are just the right distance from the Sun. In fact, Earth is at a distance at which it should be very cold. Earth has something that helps moderate its temperatures. We have an atmosphere. Without our atmosphere, the side of Earth facing the Sun in the day would be very hot and the side facing away from the Sun (nighttime) would be very cold!

Is it possible that Mercury, or the Moon, which are close to the Sun, have places that are permanently cold? If the children suggest that the side that is facing away from the Sun is cold, they are correct, but share with them that the Moon and Mercury (and other planets) spin on their axes so that all parts of the planet receive sunlight during the day and are dark at night. Share that some planets lack an atmosphere, so they cannot trap solar radiation like Earth's atmosphere and keep the planet's climate moderate. Instead, without an atmosphere, surfaces facing the Sun are HOT and surfaces that are in darkness are COLD!

Are there other places on these planets that might be cold?

What regions on Earth are the warmest, e.g. the tropical regions around the equator, the poles, or somewhere else? The equatorial regions

What regions on Earth are the coldest? The polar regions

Why do the children think this is the case?

What about other planets and moons? Do they have warmer equators and colder poles? Other planets and moons are generally warmer at their equators and colder at their poles.

Facilitator's Note: There are some exceptions. Neptune's axis is slightly tilted, like Earth's, and its south pole has pointed at the Sun for 40 years — making it the warmest spot on the planet. Curiously, the one planet that orbits the Sun on its side — Uranus — is not warmer at the pole facing the Sun than the equator. Scientists are still unsure as to why this might be the case. Saturn's moon Enceladus is also warmer at its south pole than at its equator. Its orbit around Saturn subjects the moon to tidal forces which may heat its interior and produce hot spots on its surface, including one at its south pole.

All of these bodies lie far out in the solar system where "warmer" is a relative term. The "hot spots" on these planets and moons are far below 0oF. In addition, the Sun is so far away that the difference between the temperature of the poles and equator is not as great as for the inner planets and their moons.

3. Provide the children with the clay, toothpicks, and lamps and invite them to explore why the poles are cold and the equator is warm. Have them form the clay into a ball.

As the activity will explore where ice may be on other planets or moons, what might the clay ball be? A planet or moon. In this case, the clay ball will represent our own Moon.

What might the lamp be? The Sun.

4. Have the children insert one toothpick halfway into the north pole and one toothpick halfway into the south pole of their clay Moon so that the toothpicks are perpendicular to the surface of the ball.

What do the toothpicks represent? The axis, or north and south poles of the Moon. The axis is the imaginary line that extends from the north pole of the planet through the planet to the south pole. Planets and moons spin — rotate — on their axes.

5. Invite the children to experiment with creating day and night on the Moon's surface using the lamp and ball. Day and night cycles are produced because a planet or moon spins on its axis — not because it goes around the Sun. Planets and moons do orbit the Sun, but that cycle of movement occurs over a longer timeframe and creates seasons.

6. Share that, because the Moon has no atmosphere to moderate surface temperatures, the Moon's surface that is in sunlight is very hot (average of 225°F / 107°C), and the Moon's surface that is in darkness is very cold (average of -244°F / -153°C). Areas that are shaded during the lunar day are also very cold. Let the children know also that the Moon spins more slowly on its axis than Earth. The lunar day and the lunar night each are about the length of 14 Earth days.

7. Share with the children that the Moon's axis is tilted only 1.5°; this is much smaller than Earth's axial tilt of 23.5°. As they are creating day and night, make sure they hold the Moon so that the north pole is upright and not tilted.

Where does the Sun's light most directly strike — is at the greatest angle to — the Moon's surface? At the equator; the light is the "strongest" or most direct. It gets spread out toward the poles.

Where will shadows be shortest and longest during the day on the lunar landscape?

8. Invite the children to add the rest of their toothpicks in a line stretching from the north to the south lunar pole. The toothpicks should be placed about ¾ of an inch apart, perpendicular to the surface. One toothpick should be placed at the equator of their clay Moon.

9. Invite the children illuminate their clay Moon from two to three feet away so that the center of the beam of light is aimed at the Moon's equator.

What do they observe about the shadows cast by the toothpicks? The toothpick at the equator has no shadow. The toothpicks increasingly distant from the equator have increasingly longer shadows.

What does this mean about the amount of light reaching the equator compared to the poles? The light is more direct at the equator and less direct, more spread out at the poles. There is less solar energy reaching the polar regions per unit area than at the equator. This is the primary reason why the poles of most planets and moons are colder than the equators. Of course, planets and moons that are far from our Sun receive only a small amount of incoming solar radiation, so the difference in temperature from pole to equator is not as great and may not be present.

Why is this? Because the Moon is a sphere.

Will this be the case for other planets and moons? Yes, for those that are spheres.

Are there any areas on the lunar surface that are shielded permanently from the Sun? Even at the low levels of incoming — "incident" — sunlight, the polar regions receive some light.

10. Have the children brainstorm some ideas about how they might create places that are permanently in shadow on the Moon's surface. Share the images of the cratered lunar surface.

Are the craters lit by sunlight as the Moon spins on its axis?

Are there places where craters may be lit and places where they may not be lit?

11. Invite the children to create craters in their clay moons by poking half-inch-deep holes in the surface, including several in the polar regions.

When they illuminate their clay Moon with the light, as they did earlier, what do they observe about the light in the cratered regions?

Is there a difference between craters at the pole and craters at the equator? Craters across much of the surface are illuminated by the light, but the bottoms of craters at the poles stay dark all the time.

What does this mean for the temperature in the craters that stay dark? These craters do not receive any light or energy from the Sun, so they are very cold.

Scientists have reported that ice may exist in some of the deep, dark, cold craters at the Moon's north and south poles. They suggest that even Mercury may have ice at its poles. New NASA missions, like the MESSENGER mission to Mercury and the Lunar Reconnaissance Orbiter and the Lunar Crater Observation and Sensing Satellite missions to the Moon will help us find out if ice is in these places!

Where might the ice have come from? Can the children think of any small icy bodies in our solar system that may occasionally run into a planet or moon? Comets!Scientists have evidence that comets do strike planets (we observed Comet Shoemaker-Levy hitting Jupiter!). These comets can bring water and ice to the planets they strike.

12. Tell the children that two comets are about to strike their Moon. Provide the groups with two ice cubes. Have them place once in a crater at the north pole and one in a crater at the equator. Make sure to push the ice cubes into the clay so that they are beneath the surface with the tops of the cubes exposed. This will help them stay in place.

Which ice cube will melt faster when the Sun's radiation (from the lamp) reaches the planet: the ice cube at the pole or the one at the equator?

13. Invite the children to illuminate their Moon, holding the lamp about 5 to 6 inches from the surface, for about three minutes. The child holding the Moon should hold it so that his or her fingers are as far from the ice cubes as possible.

Where is the solar radiation striking the surface most directly? The middle of the planet at the equator.

What affect do they think this is having on the ice cube that is imbedded at the equator?

What about the ice cube imbedded at the pole?

The children may notice that the ice cube at the pole is melting slightly. This is not the case for ice in permanently shadowed regions on the Moon!

Why might they observe the ice at the pole in their model melting a little, but in permanently shadowed areas of the Moon it does not melt? In the experiment, the ice is in a room that is warmer than the freezing point of water, so the ice melts. On the Moon there is no atmosphere to hold solar radiation, so it is very cold in the dark and very hot in the sunlight. Permanently dark areas are permanently cold.

14. After three minutes have the children remove the ice cubes and examine them.

Do they see a difference in the size of the two ice cubes now? The ice cube at the equator melted more and should be significantly smaller.

Why did this happen? The ice cube at the equator received more direct solar radiation (heat from the lamp). The ice cube at the pole received less direct, more diffuse solar radiation.

In Conclusion

Have the children reflect on where ice might be in the solar system based on what they know about ice and what they have learned in the experiment.

What does ice need to exist on a planet? Temperatures that are sufficiently cold.

What planets have surface temperatures that are cold enough for ice?

Are there planets that are "too hot" — too close to the Sun — to have ice?